Certain modern vehicles are equipped with some form of camera which is capable of showing a picture of the area behind the vehicle. Such a camera can make it easier for a driver to reverse drive the vehicle, which is the primary object of equipping passenger cars with such cameras. For heavier vehicles, such as trucks, buses and the like, this obviously also facilitates reversing, but in this case such a camera also has a safety-enhancing effect by showing what is situated immediately behind the vehicle, where the view is otherwise obscured.
For heavier vehicles the reversing camera makes it possible to see what is situated immediately behind the vehicle. This may be of help not only in seeing whether a person is standing behind the vehicle, for example, but also in marshalling the vehicle. In marshalling a vehicle it is a question of placing the vehicle in a desired position with as little deviation as possible; for example, where a vehicle with tail lift is being reversed towards a loading platform. Another example is when a tractor vehicle is to couple up to a trailer vehicle.
In its simplest embodiment a reversing camera is an ordinary analog video-camera that shows a picture on a display screen. Digital reversing cameras also exist in which the picture can either be shown directly on a display screen or in which the picture may first undergo some form of signal processing in a control unit before being shown on the display screen. The signal processing may consist, for example, of adjusting the contrast and brightness of the picture so that a clear, useable picture is obtained regardless of the weather and time of day. Reversing cameras are often equipped with wide-angle lenses which give a distorted image, for which reason the control unit can also compensate for display defects of the wide-angle lens.
WO 0124527, EP 1022903, JP 2002019492 and JP 2000280822 describe systems to facilitate the reversing of a passenger car in which, among other things, a predicted vehicle movement, estimated by measuring the angle of the vehicle wheel deflection, is shown on the display screen. JP 2001010431 furthermore describes a method of displaying a guide line which is constantly adjusted to the angle of the vehicle wheel deflection. This varying guide line is intended to facilitate parking of the passenger car. US 20020149673 A1 describes an apparatus to assist a driver in reversing a vehicle having a tow ball towards a trailer vehicle with a ball coupling.
These methods may perhaps make reversing easier for inexperienced drivers, and they can possibly function satisfactorily in the case of passenger cars where the camera is in a known, fixed location low down. For heavy vehicles each individual vehicle would need to be programmed separately since the reversing camera has a different location depending on the type of vehicle and equipment.
Furthermore, the documents cited do not solve the problem of making it easier to position a vehicle into a desired position when marshalling the vehicle. The systems described are only designed to operate when reversing the vehicle, not when the vehicle is being marshaled, nor does the driver receive any help in positioning a component fitted to the vehicle in relation to a desired position when marshalling the vehicle.